Do folk drop the 3D print into simple, clean, dry sand with a sprue for lost positive casting? Would there be any advantage in casting the positive in greensand?
Lost pla casting is not a sand casting process like lost foam casting rather it is an investment casting process meaning the pattern is embedded in a plaster or ceramic based mold material then the pattern and mold are fired to burn out the pattern leaving behind a hollow mold into which molten metal can then be poured.
I tried making “shell” with sodium silicate to cast PLA patterns that did not have proper draft for standard sand casting. The PLA was not burned out in my experiment. But I think it could have been. In my case I cooked the PLA/silicate mold and pulled out the gooey PLA. It worked. It could be an alternative if circumstances warranted it. http://forums.thehomefoundry.org/index.php?threads/heating-pla-patterns-to-facilitate-removal-from-sodium-silicate-molds.808/ Denis
Interesting. So basically that would be using silicate bonded sand as the investment, somebody here needs to try that to see if it's a viable method.